Salmonella typhimurium strains TA-98, TA-100, TA-1535, and TA-1537 are being used to test selected chemicals of interest for mutagenicity. Natalan, an antineoplastic drug which is mutagenic in eukaryotic cells was not mutagenic in these strains even at levels which produced cell killing. A series of cyclic hydrazides which are analogues of cyclic nitrosamines are being tested for mutagenicity for comparison with their mutagenic and non-mutagenic nitrosamine counterparts. N-aminopiperidine and N-aminomorpholine were both mutagenic, producing only base-pair substitution mutations in the presence and absence of rat liver S-9; however, more activity was seen in the absence of S-9. N-aminomorpholine was significantly more mutagenic than N-aminopiperidine.